Spline

Draw a smooth curve that passes through a series of points.

This function allows you to draw a spline by entering the points the spline curve must pass through.

The smooth curve created is known as a Nonuniform Rational B-Spline (NURBS).

An existing spline can be edited by selecting it and then choosing edit options from the right-click context menu.

The drawn spline function creates a spline using fit points, but there is also full access to the control points and weight available through the Property Bar.

Procedure

To draw a smooth curve to pass through a series of points:

1. Select Draw ► Splines or click the icon in the Drawing toolbar.

2. You are prompted to:

Indicate first point

3. Position the cursor over the desired start position and click or press [Enter].

4. You are prompted to:

Indicate second point

A rubberbanded line shows.

5. Click on the position of the second point. You are prompted to:

Indicate next point (Right-click to end)

6. Enter the required points of the curve by clicking or pressing [Enter] on the desired position. You can jump to the desired point or use the snaps.

7. Once you have finished drawing the curve, right-click to open the context menu. You have four options to select from when drawing the spline.

Close

1. Select Close if you want the spline to start and end on the same point, and completely enclose at least one area. The spline is updated and a rubberband shows a line from the start of the spline to the cursor. This represents the tangent at the start of the spline.

2. You are prompted to:

Indicate tangent

To maintain continuity, the start and end tangent are the same for a closed spline.

3. To select the tangent, click on the desired position for the tangent.

4. If you do not want to specify the tangent, right-click and select Skip Tangent from the context menu.

5. The spline is now drawn in as shown below.

Finish

You can select Finish when you have completed entering the fit point and do not want the spline to be closed.

1. Select Finish.

2. You are prompted to:

Indicate starting tangent

The rubberband shows a line from the start of the spline to the cursor representing the tangent at the start of the spline. The spline updates to show how the tangent affects the final entity as the cursor is moved.

3. Enter on the position for the tangent. The line is now joined to the end tangent point.

4. You are prompted to:

Indicate ending tangent

The rubberband shows a line from the end of the spline to the cursor representing the tangent at the end of the spline. The spline updates to show how the tangent affects the final entity as the cursor is moved.

5. Enter on the position for the tangent.

You can also right-click on the screen after selecting finish and select Skip Start Tangent, Skip Both Tangents or Skip End Tangent from the Context menu.

The first two are available from the Context menu when choosing the start tangent and the last when choosing the end tangent.

6. The spline is updated, as shown below.

7. The function repeats and you can start drawing the next spline.

8. Right-click and select Quit to end the function. Alternatively, press [Esc].

9. You can now double-click the spline to open the Properties window. Here you can edit the Control Points and Fit Points of the spline, as well as the Weight.

10. If you have the selection handles in the System Settings turned off you will see the Fit Points as indicated on the drawing below .

11. If you click the Fit Points text in the Properties window, spin arrows appear. You can now change the position of the Fit Point using the spin arrows.

Here the Fit Point has changed to position 3.

12. You can edit any of the Fit Points' X,Y or Z coordinates in the Properties window. Select the point to edit and type the new position, or click and drag any of the Fit Points on the screen to a new position as shown below. This changes the curve of the spline.

13. To edit the Control Points, select Use Fit Points in the Properties window and set it to No.

This allows you to edit the Control Points, as shown below.

14. If you click on the Control Points text in the Properties window, spin arrows appear. You can change the position of the Control Point using the spin arrows and edit any of the Control Point's X,Y or Z coordinates in the Properties window. Select the point to edit and type the new position, or click and drag any of the Control Points on the screen to a new position, as shown below.

This changes the curve of the spline.

15. You can change the curve by editing the Weight in the Properties window. The Weight of Control Point 4 has been changed to 0.4 in the below example.

The Weight of Control Point 4 has been changed to 4 in the below example. Note the difference.

16. You can edit the curve by switching the selection handles on and moving any of the Grips shown below.

17. Right-click and select Quit to end the function. Alternatively, press [Esc].

Editing an Existing Spline

The following options are used to edit an existing spline.

Append a Fit Point

1. Select the spline entities you created by clicking near it.

2. Right-click and select Append Fit Point from the popup menu.

3. Click on your desired location and a new fit point is created, which extends the original spline.  The updated spline is extended either from the beginning or the end of the spline with regard to which end of the spline is closer to the left-click point.  

4. Right-click and select Quit from the popup menu to finish this operation.

This function is invalid for a closed spline.

Insert a Fit Point

1. Select the spline entities you created by clicking near it.

2. Right-click and select Insert Fit Point from the popup menu.

3. Click on your desired location and a new fit point is inserted inside the spline.  The shape of the spline is updated accordingly.

4. Right-click and select Quit  to finish this operation.

Remove a Fit Point

1. Select the spline entities you created by clicking near it.

2. Right-click and select Remove Fit Point from the popup menu.

3. Click around the fit point you want to remove. The shape of the spline is updated accordingly.

4. Right-click and select Quit  to finish this operation.

This function is invalid for a spline with less than three fit points.